Geoscience Reference
In-Depth Information
between the various regions appear to be highly complex. To understand the
dynamics of the whole system with all its interrelationships at various levels of
complexity is one of the most important reasons to use first-principle models for
their description. They allow us to perform “numerical experiments” and to interpret
different measurements on a common basis, which may be obtained at various
places far from each other by both ground-based observations and remote or in situ
data gathering with satellites.
This chapter presents and discusses some of the most recent measurements
of the near-Earth environment obtained by Cluster, CHAMP, and the global
positioning system (GPS) satellites and their modeling in the framework of the
Upper Atmosphere Model (UAM). The results concern ionospheric electric fields,
generated by magnetospheric and seismogenic sources, and show their influence on
the thermospheric dynamics and the ionospheric total electron content (TEC).
4.2
UAM: The Upper Atmosphere Model
The global numerical model of the Earth's upper atmosphere has been constructed at
the Kaliningrad Observatory (now West Department) of the Institute of Terrestrial
Magnetism, Ionosphere and Radiowave Propagation of the Russian Academy of
Sciences (IZMIRAN) (Namgaladze et al.
1988
,
1990
,
1991
,
1994
) and modified
at the Polar Geophysical Institute and Murmansk State Technical University (Hall
et al.
1997
; Namgaladze et al.
1995a
,
b
; Volkov and Namgaladze
1996
). The model
describes the thermosphere, ionosphere, plasmasphere, and inner magnetosphere of
the Earth as a single system by means of numerical integration of the corresponding
time-dependent three-dimensional continuity, momentum, and heat balance equa-
tions for neutral, ion, and electron gases as well as the equation for the electric field
potential. It covers the height range from 60 (sometimes 80) km up to 15 Earth radii
of geocentric distance and takes into account the offset between the geomagnetic
and geographic axes of the Earth. It consists of four main blocks:
1. The neutral atmosphere and lower ionosphere block, which calculates neutral
atmosphere temperature, mass density, neutral gas composition, and winds as
well as ion and electron temperatures, molecular ion density, and velocity at
heights from 60 to 520 km
2. The ionospheric F2-region and protonospheric block, which calculates atomic
ion O
C
and H
C
densities, velocities, and temperatures as well as electron
temperature at heights from 175 km to 15
R
E
of geocentric distance
3. The electric field block, which calculates the electric field potential of magne-
tospheric, thermospheric (dynamo), and lower atmosphere origin, assuming that
geomagnetic field lines are equipotential at heights above 175 km
4. The magnetospheric block, which calculates magnetospheric plasma sheet ion
density, velocity, pressure, and field-aligned currents at the same heights as in
the second block
